Cancer stem cells (CSC) have been identified in an increasing number of human malignancies, and their enhanced growth potential has suggested that they play a major role in disease initiation, maintenance, relapse and progression. We hypothesize that better understanding CSCs will ultimately improve long-term clinical outcomes and have begun to study CSC in pancreatic adenocarcinoma, a leading cause of cancer deaths. We have found that pancreatic cancer cells with increased tumorigenic potential express aldehyde dehydrogenase (ALDH), a detoxifying enzyme expressed by many normal stem cells. Moreover, ALDH+ cells express genes consistent with the epithelial-mesenchymal transition and are more invasive and migratory when compared to bulk tumor cells. We have also compared ALDH+ cells with CD44+CD24+ cells that have also been identified by others as pancreatic CSC and found that each phenotype marks distinct cell populations that are largely non- overlapping. Interestingly, each CSC population is equally capable of forming tumors, but ALDH+ cells are often more migratory and invasive. Based on these findings, we hypothesize that individual tumors contain distinct CSC populations that may or may not share specific functional properties. Moreover, these findings suggest that CSCs may vary amongst pancreatic tumors from different patients depending on their specific genetic mutations or stage of disease. Since the development of CSC targeting strategies requires their precise identification, it is imperative that the relationship between their phenotype and functional properties and the factors that influence this relationship are better understood. Moreover, it is likely that extracellular signals within the tumor microenvironment regulate CSC properties, but this is also poorly understood. We propose to address these questions and will: (1) Define the relationship between distinct CSC populations in pancreatic cancer; (2) Examine the cellular diversity of pancreatic CSC; and (3) Determine whether interactions between pancreatic CSCs and the extracellular matrix can serve as novel CSC targeting strategies.